Device for the purification of machining liquids for electroerosion machines

ABSTRACT

The device for purifying machining liquids for electroerosion machines, comprises a first ultrasonic decantation device ( 11 ) to separate by decantation the metallic contamination particles ( 38 ) from the machining electrode and the machined piece, a second ultrasonic decantation device ( 45 ) of a lower power to separate the particles ( 39 ) of said machining additive, and filtration elements ( 46 ) to separate carbonaceous particles ( 41 ) from the decomposition of the dielectric liquid. After filtration, this latter is remixed with the additive particles in a mixing receptacle ( 47 ) to obtain purified machining liquid.

[0001] The present invention relates to a device for the purification ofmachining liquids for electroerosion machines provided with an electrodeadapted to machine a piece, the machining liquid being constituted by adielectric liquid containing at least first particles of an additiveadapted to facilitate electroerosion and second particles ofcontamination from the electrode and/or the piece and having a higherdensity than the first particles.

[0002] It has been demonstrated that, during machining with anelectroerosion machine, the use of an additive in the form of a powderhaving particles of the order of several microns, greatly improves themachining performance, see for example Swiss patent 670,785.

[0003] During machining by electroerosion with powder and particles asadditives, the principal element not solved is the filtration andpurification of the used and contaminated machining liquid.

[0004] There are encountered in this latter, particles of the additive,particles in the form of metallic spherules of the material of the pieceand of the electrode, as well as particles of colloidal carbon in theform of submicron size in the case of carbonated dielectric liquids.

[0005] An ideal filtration should retain only the dielectric liquid andthe particles of additive. Conventional filtrations however do notpermit obtaining the desired filtration, because a coarse filtration(>20 μm) lets pass many fine metallic spherules. On the contrary, a finefiltration eliminates, in addition to the metallic spherules, theadditive powders. A magnetic separation works only for magnetic metallicspherules, but not for all the other spherules.

[0006] The present invention has for its object to overcome thesedrawbacks and to provide a purification device permitting obtaining ahigh degree of purification and this with means that are simple to useand at a moderate cost. The invention is characterized to this end bythe fact that the device comprises at least one ultrasonic decantationdevice comprising a first decantation receptacle for the machiningliquid in which is disposed a first ultrasonic emission member connectedto a first ultrasonic generator whose power can be adjusted such thatthe second particles decant whilst the first particles remain insuspension in the dielectric liquid.

[0007] These characteristics permit obtaining a good purification ofmachining liquids and a device of moderate cost which is simple to useand rapid and reliable in operation.

[0008] The device moreover can comprise preferably means for supplyingcontaminated machining liquid to the first decantation receptacle and atleast one opening provided in this latter for the discharge of purifiedmachining liquid containing the first particles.

[0009] According to a preferred embodiment, the device comprisessupplemental means to separate third contamination particles constitutedby colloidal carbon from the decomposition of the machining liquid,these supplemental means comprising a second ultrasonic decantationdevice with a second decantation receptacle in which is disposed asecond ultrasonic emission member connected to a second ultrasonicgenerator, the power of this latter being adjusted such that the firstparticles decant, whilst the third particles remain in suspension in themachining liquid, this second decantation receptacle comprising an inletconnected to said opening.

[0010] This embodiment is particularly well adapted for the processingof carbonated dielectric machining liquids, such as oil, which permitpurifying to a high degree of purity.

[0011] Preferably, the supplemental means comprise a mixing receptaclehaving mixing members, filtration elements for the machining liquidobtained by decantation at the outlet of the second decantationreceptacle and arranged to retain by filtration the third particles, afiltered dielectric liquid supply conduit from the filtration elementsto said mixing receptacle, and extraction and transport means arrangedto transport the first decanted particles from the second decantationreceptacle to the mixing receptacle.

[0012] By these characteristics, the carbonated dielectric liquids canbe purified effectively and reconstitution of the complete machiningliquid can be carried out in a reliable and inexpensive manner.

[0013] Other advantages will become apparent from the characteristicsset forth in the dependent claims and from the description givenhereafter of the invention, in greater detail, with the help of thedrawings which show schematically and by way of example two embodiments.

[0014]FIGS. 1 and 2 are schematic views of a first and secondembodiment.

[0015] With reference to FIG. 1, electroerosion machine 10 is providedwith a first embodiment of the decantation device 11.

[0016] This electroerosion machine comprises a working receptacle 12 inwhich is contained a machining liquid 14 and a piece 15 to be machinedmounted on a work table 16. The electroerosion machine moreover has anelectrode 17 serving as a machining tool, mounted on a spindle 18.

[0017] The machining liquid 14 is circulated and temperature controlledin the working receptacle 12 thanks to a mixing installation 20comprising a pumping circuit 21 with a suction pump 22 and a heatexchanger 23 connected to a cooling water circuit.

[0018] The machining liquid 14 is constituted by a dielectric liquid inwhich are suspended first particles of an additive adapted to facilitateelectroerosion and second particles of contamination from the electrodeand/or the piece 15 to be machined. The first particles could forexample be graphite particles of a density of 2 to 2.2 g/cm and agranulometry between 1 and 100 μm, preferably between 1 and 10 μm. Thesecond particles are generally present in the form of metallic spherulestorn off and ejected from the piece to be machined and from theelectrode during erosive discharges. Their density, greater than that ofthe first particles, is comprised between 4 and 20 g/cm³.

[0019] The granulometry of these spherules is generally comprisedbetween 1 and 40 μm.

[0020] When the dielectric liquid is of a carbonated nature, themachining liquid can moreover comprise third particles in the form ofparticles of colloidal carbon caused by the decomposition of thedielectric liquid under the influence of the erosive discharges, whichhave the tendency to flocculate in submicron particles. The density ofthese third particles is less than 2 g/cm³ and their diameter isgenerally less than 0.5 μm. Of course these third particles do not existin the case of water as the dielectric liquid.

[0021] The first embodiment of the decantation device 11 has adecantation receptacle 30 for the machining liquid in which is disposedan ultrasonic emission member 30 in the form of a sonotrode. This latteris connected by a connection 32 to an ultrasonic generator 33 of afrequency of 40 kHz and whose power can be adjusted, for example from 10to 200 watts. A conduit 34 provided with a suction pump 35 serves assupply means for the contaminated machining liquid into the decantationreceptacle 30. At least one opening 36 connected to an outlet conduit 37permits returning the machining liquid purified from the secondcontamination particles, to the electroerosion machine, either into anattached reservoir, or directly into the working receptacle.

[0022] Ultrasound is a very effective way to place in suspensionparticles of the size of the first particles of the additive powders.The ultrasonic energy for suspending the particles must be higher thegreater is the density of the particles and the greater is their size.It is to be noted that below a critical size, the density has lessimportance than the size for suspending by diffusion. Decantation ismoreover slowed when the viscosity of the machining liquid increases. Itis thus possible to provide a selective decantation device operated bymoderate ultrasonic energy. The power of the ultrasonic generator 30 isadjusted for each density and viscosity of the machining liquid and eachdensity and size of the particles to be separated. The optimumadjustment permits decantation and accumulation on the bottom of thedecantation receptacle, of the second contamination particles 38, namelythe metallic spherules, whilst keeping in suspension the first particles39 that are lighter, of the additive, such as graphite.

[0023] The power of this generator 33 is thus generally adjusted between10 and 150 watts, preferably between 4 and 100 watts.

[0024] Such a decantation device suffices for the case of water as thedielectric liquid, it can also be used in this form if it is acceptableto let the first particles subsist with the third particles of carbonfrom the decomposition of a carbonated dielectric liquid, such as oil.

[0025] The separation and elimination of the third particles requires amore complete purification device, of which one embodiment is describedwith reference to FIG. 2.

[0026] This second embodiment comprises a first decantation device 11identical or similar to that described with reference to FIG. 1. It ismoreover provided with supplemental means 40 adapted to separate thethird contamination particles 41 of the machining liquid from which hasalready been decanted the second particles 38. These supplemental meanscomprise a second decantation device 45, filtration elements 46 and amixing receptable 47.

[0027] The second decantation device 45 comprises for this purpose asecond decantation receptacle 50 in which is disposed a secondultrasonic emitting member 51, in the form of a second sonotrodeconnected by a connection 52 to a second ultrasonic generator 53.

[0028] The outlet conduit 37 of the first decantation device 11 servesas a supply conduit for the machining liquid containing the first andthird particles.

[0029] The second ultrasonic generator 53 has a frequency of 40 kHz andits power can be adjusted for example between 1 and 30 watts, preferablybetween 5 and 20 watts. Its power is thus adjusted to be lower than thatof the first generator 33. It is adjusted to maintain in suspension thethird particles 41, whilst the first particles decant and accumulate ona conveyor belt 55 serving as an extraction and transport means to bringthese first particles 39 above the mixing receptacle 47, where they aredischarged.

[0030] An outlet conduit 56 provided with a pump 57 supplies machiningliquid with third particles 41 to the filtration elements 46. Theselatter are arranged to retain all the third particles 41 and comprise tothis effect at least one fine filter, for example a paper cartridgefilter. The dielectric liquid 58 thus purified is conveyed by a conduit59 into the mixing receptacle 47, where it is mixed with the firstparticles by mixing members 60, such as paddles or air circulation, etc.The purified and thus constituted machining liquid is then returned by apipe 61 and a pump 62 to the electroerosion machine.

[0031] These purification devices are particularly important for roughmachining and for semi-finishing and permit eliminating the largestmetallic particles which would otherwise be very troublesome duringsubsequent finish machining.

[0032] Of course, the embodiments described above are in no way limitingand can be the subject of any modification desirable within the scopedefined by claim 1. In particular, other devices could be added, such aswashing or any other treatment of the first additive particles leavingthe second decantation receptacle 50, a measured supplier for the firstparticles permitting obtaining an exact concentration of the firstparticles in the machining liquid contained in the mixer 47, anextraction device, for example a conveyor, for the second metallicparticles of contamination into the first decantation receptacle 30. Allof the purification device could be integrated into the electroerosionmachine or constitute a unit separate from this latter.

1. Device for purifying machining liquids for electroerosion machines(10) provided with an electrode (17) adapted to machine a piece (15),the machining liquid (14) being constituted by a dielectric liquidcontaining at least first particles (39) of an additive adapted tofacilitate electroerosion and second particles (38) of contaminationarising from the electrode (17) and/or from the piece (15) and having ahigher density than the first particles (39), characterized by the factthat the device comprises at least one ultrasonic decantation device(11) comprising a first decantation receptacle (30) for the machiningliquid (14) in which is disposed a first ultrasonic emission member (31)connected to a first ultrasonic generator (33) whose power can beadjusted such that the second particles (38) decant, whilst the firstparticles (39) remain in suspension in the dielectric liquid.
 2. Deviceaccording to claim 1, characterized by the fact that it comprises supplymeans (34, 35) for supplying contaminated machining liquid into thefirst decantation receptacle (30) and at least one opening (36) providedin this latter for discharging purified machining liquid containing thefirst particles (39).
 3. Device according to claim 2, characterized bythe fact that it comprises supplemental means (40) to separate thirdparticles (41) of contamination constituted by colloidal carbon from thedecomposition of the machining liquid, these supplemental means (40)comprising a second ultrasonic decantation device (45) with a seconddecantation receptacle (50) in which is disposed a second ultrasonicemission member (51) connected to a second ultrasonic generator (53),the power of this latter being adjusted such that the first particles(39) decant, whilst the third particles (41) remain in suspension in themachining liquid, this second decantation receptacle (50) comprising aninlet connected to said opening (36).
 4. Device according to claim 3,characterized by the fact that the supplemental means (40) comprise amixing receptacle (47) with mixing members (60), filtering elements (46)for the machining liquid obtained by decantation at the outlet of thesecond decantation receptacle (50) and arranged to retain by filtrationthe third particles (41), a supply conduit (59) for the filtereddielectric liquid from the filtration elements (46) to said mixingreceptacle (47) and extraction transport means (55) arranged totransport the first particles (39) decanted from the second decantationreceptacle (50) into the mixing receptacle (47).
 5. Device according toclaim 4, characterized by the fact that said extraction and transportmeans are constituted by a conveyor belt (55) arranged in the bottom ofthe second decantation receptacle (50) and extending just above themixing receptacle (47) to discharge the first particles (39) into thislatter.
 6. Device according to claim 3, characterized by the fact thatthe first ultrasonic generator (33) is adjusted to a power comprisedbetween 10 and 50 watts, preferably between 40 and 100 watts, and by thefact that the second ultrasonic generator (53) is adjusted to a lowerpower, comprised between 1 and 30 watts, preferably between 5 and 20watts.